RocketChat/Rocket.Chat

import { RandomGenerator } from './RandomGenerator';

// Alea PRNG, which is not cryptographically strong
// see http://baagoe.org/en/wiki/Better_random_numbers_for_javascript
// for a full discussion and Alea implementation.
function createAlea(seeds: readonly unknown[]) {
    function createMash() {
        let n = 0xefc8249d;

        const mash = (data: unknown) => {
            data = String(data);
            if (typeof data !== 'string') {
                throw new Error('Expected a string');
            }

            for (let i = 0; i < data.length; i++) {
                n += data.charCodeAt(i);
                let h = 0.02519603282416938 * n;
                n = h >>> 0;
                h -= n;
                h *= n;
                n = h >>> 0;
                h -= n;
                n += h * 0x100000000; // 2^32
            }
            return (n >>> 0) * 2.3283064365386963e-10; // 2^-32
        };

        mash.version = 'Mash 0.9';
        return mash;
    }

    let s0 = 0;
    let s1 = 0;
    let s2 = 0;
    let c = 1;
    if (seeds.length === 0) {
        seeds = [+new Date()];
    }
    const mash = createMash();
    s0 = mash(' ');
    s1 = mash(' ');
    s2 = mash(' ');

    for (let i = 0; i < seeds.length; i++) {
        s0 -= mash(seeds[i]);
        if (s0 < 0) {
            s0 += 1;
        }
        s1 -= mash(seeds[i]);
        if (s1 < 0) {
            s1 += 1;
        }
        s2 -= mash(seeds[i]);
        if (s2 < 0) {
            s2 += 1;
        }
    }

    const random = () => {
        const t = 2091639 * s0 + c * 2.3283064365386963e-10; // 2^-32
        s0 = s1;
        s1 = s2;
        s2 = t - (c = t | 0);
        return s2;
    };

    random.uint32 = () => random() * 0x100000000; // 2^32
    random.fract53 = () => random() + ((random() * 0x200000) | 0) * 1.1102230246251565e-16; // 2^-53

    random.version = 'Alea 0.9';
    random.args = seeds;
    return random;
}

// options:
// - seeds: an array
//   whose items will be `toString`ed and used as the seed to the Alea
//   algorithm
export class AleaRandomGenerator extends RandomGenerator {
    private readonly alea: () => number;

    constructor({ seeds = [] }: { seeds?: readonly unknown[] } = {}) {
        super();
        if (!seeds) {
            throw new Error('No seeds were provided for Alea PRNG');
        }
        this.alea = createAlea(seeds);
    }

    /**
     * @name Random.fraction
     * @summary Return a number between 0 and 1, like `Math.random`.
     * @locus Anywhere
     */
    fraction() {
        return this.alea();
    }

    protected safelyCreateWithSeeds(...seeds: readonly unknown[]): RandomGenerator {
        return new AleaRandomGenerator({ seeds });
    }

    insecure: RandomGenerator = this;
}